This invention belongs to the field of polycarbonates. In particular, it relates to polycarbonate copolymers having improved solvent resistance, improved hydrolytic stability, or combinations thereof.
Polycarbonates in general are prepared from dihydric phenol compounds and carbonic acid derivatives. For example, one important polycarbonate can be prepared via melt polymerization of diphenyl carbonate and Bisphenol A. The reaction is conducted at high enough temperatures for the starting monomers and product to remain molten, while the reactor pressure is staged in order to effectively remove phenol, the by-product of the polycondensation reaction.
Condensation polymers such as the polycarbonates are susceptible to hydrolytic degradation, especially under certain environmental exposures. In particular, when polycarbonate is utilized as an internal structural component in dishwashers, the polycarbonate material is regularly exposed to dilute caustic solution, which has deleterious effects on the polymer structure over time. Further, many polycarbonates are utilized in applications which involve exposure to organic solvents.
Thus, a need exists for polycarbonates having improved hydrolytic stability, especially against dilute caustic solution as well as resistance to organic solvents.
The present invention provides polycarbonate copolymers having improved hydrolytic stability, solvent resistance, or combinations thereof. In particular, certain of the copolymers of the invention have improved resistance to dilute caustic solution, while others show improved solvent resistance. Thus, the copolymers of the present invention are particularly useful as structural elements in applications where such elements routinely come in contact with caustic solutions, such as in automatic dishwashing equipment. Preferred comonomers include 4,4xe2x80x2-biphenol, bis-(4-dihydroxyphenyl)terephthalamide (xe2x80x9cBHPTxe2x80x9d), and a bisimide bisphenol obtained by reacting Bisphenol A dianhydride (BPADA) with 4,4xe2x80x2-isopropylidene phenol aniline. The comonomers are utilized along with 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A) in concentrations in a range between about 1 weight percent and about 50 weight percent of repeating units in the polycarbonate based on total dihydric phenol.
In this application:
The singular forms xe2x80x9ca,xe2x80x9d xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise.
xe2x80x9cOptionalxe2x80x9d or xe2x80x9coptionallyxe2x80x9d means that the subsequently described event or circumstances may or may not occur, and that description includes instances where the event or circumstance occurs and instances where it does not.
xe2x80x9cBPAxe2x80x9d is herein defined as Bisphenol A or 2,2-bis(4-hydroxyphenyl)propane.
Unless otherwise stated, xe2x80x9cweight percentxe2x80x9d in reference to the composition of a polycarbonate in this specification is based upon 100 weight percent of the repeating units of the polycarbonate. For instance, xe2x80x9ca polycarbonate comprising 90 weight percent of BPAxe2x80x9d refers to a polycarbonate in which 90 weight percent of the repeating units are residues derived from Bisphenol A or its corresponding derivative(s). Corresponding derivatives include, but are not limited to, corresponding oligomers of the diphenols; corresponding esters of the diphenol and their oligomers; and the corresponding chloroformates of the diphenol and their oligomers.
Thus, in one aspect, the present invention provides a polycarbonate comprised of residues of;
(a) a diester compound; and
(b) a dihydric phenol compound, wherein said dihydric phenol compound(s) are comprised of
(i) 2,2-bis(4-hydroxyphenyl) propane;
(ii) at least one comonomer in a range between about 1 weight percent and about 50 weight percent of the repeating units in the polycarbonate, comprising bis-(4-hydroxyphenyl)-terephthalamide, bis-(3-hydroxyphenyl)terephthalamide, a compound of the formula 
xe2x80x83wherein X is a divalent aromatic moiety; and
(iii) optionally, dihydric phenol compounds in addition to those in (i) and (ii).
The polycarbonate is formed via a polycondensation reaction.
Examples of divalent groups (X) include phenylene, naphthalene, and groups of the formula 
(i.e., xe2x80x9cBisimide BPAxe2x80x9d or BIABPA) as well as such groups optionally substituted by one or more groups selected from C1-C8 alkyl, C1-C8 alkoxy, halo, nitro, and the like.
The utilization of the above monomers provides, in certain cases, improved hydrolytic stability to the polycarbonate compositions and in certain cases improved solvent resistance. In an alternate embodiment of the present invention, the monomers in paragraph (ii) above are utilized in proportions in a range between about 1 weight percent and about 40 weight percent of the repeating units in the polycarbonate with no greater than 15 weight percent of any one given comonomer. In a further alternate embodiment of the present invention, the monomers in paragraph (ii) above are utilized in a range between about 1 weight percent and about 5 weight percent of the repeating units in the polycarbonate. In this regard, the use of the term xe2x80x9cresiduexe2x80x9d denotes that portion of the molecule or moiety which remains after the polycondensation reaction has taken place.
The structure of bis-(4-hydroxyphenyl)terephthalamide and bis-(3-hydroxyphenyl)terephthalamide (BHFF) are as follows, respectively: 
Certain combinations of comonomers result in melt phase-produced polycarbonates having improved hydrolytic stability. In particular, when the comonomers illustrated above in this first aspect of the present invention are utilized with 4,4xe2x80x2-biphenol, hexafluoro Bisphenol A, or combinations thereof, the resulting polycarbonates exhibit improved hydrolytic stability. Thus, in a typical embodiment of this first aspect of the present invention, there is provided the polycarbonates of the first aspect, further comprising at least one comonomer selected from 4,4xe2x80x2-biphenol and a compound of the formula 
In a typical embodiment of the present invention, the 4,4xe2x80x2-biphenol, hexafluoro Bisphenol A, or combinations thereof, are utilized in an amount in a range between about 1 weight percent and about 15 weight percent of the repeating units in the polycarbonate.
4,4xe2x80x2-Biphenol alone as a comonomer in conjunction with Bisphenol A in a melt phase-produced polycarbonate is useful in effecting an increase in hydrolytic stability. Thus, in a second aspect of the present invention, there is provided a polycarbonate comprised of residues of;
(a) a diester compound; and
(b) a dihydric phenol compound, wherein said dihydric phenol compound(s) are comprised of
(i) 2,2-bis(4-hydroxyphenyl) propane; and
(ii) 4,4xe2x80x2-biphenol in a range between about 1 weight percent and about 30 weight percent of the repeating units in the polycarbonate.
In this regard, 4,4xe2x80x2-biphenol is commonly in an amount in a range between about 1 weight percent and about 15 weight percent of the repeating units in the polycarbonate.
4,4xe2x80x2-Biphenol, when utilized with certain other comonomers, results in improved hydrolytic stability in melt phase-produced polycarbonates. Thus, in third aspect, the present invention provides a polycarbonate comprised of residues of;
(a) a diester compound; and
(b) a dihydric phenol compound, wherein said dihydric phenol compound(s) are comprised of
(i) 2,2-bis(4-hydroxyphenyl) propane; and
(ii) comonomers in a range between about 1 weight percent and about 50 weight percent of the repeating units in the polycarbonate, comprising 4,4xe2x80x2-biphenol and a compound of the formula 
wherein X is a group of the formula 
wherein the proportion of 4,4xe2x80x2-biphenol is in a range between about 1 weight percent and about 15 weight percent of the repeating units in the polycarbonate.
BIABPA, when utilized as a comonomer in a melt phase-produced polycarbonate, provides improved hydrolytic stability. Thus, in a fourth aspect of the present invention, there is provided a polycarbonate comprised of residues of;
(a) a diester compound; and
(b) a dihydric phenol compound, wherein said dihydric phenol compound(s) are comprised of
(i) 2,2-bis(4-hydroxyphenyl) propane; and
(ii) a comonomer in a range between about 1 weight percent and about 50 weight percent of the repeating units in the polycarbonate, of the formula 
xe2x80x83wherein X is a group of the formula 
In this fourth aspect of the present invention, it is especially typical that the BIABPA is utilized in a range between about 1 weight percent and about 15 weight percent of the repeating units in the polycarbonate.
Bis-(4-hydroxyphenyl)terephthalamide in a melt phase-produced polycarbonate yields polycarbonates having improved solvent resistance. Thus, in a yet a fifth aspect of the present invention, there is provided a polycarbonate comprised of residues of;
(a) a diester compound; and
(b) a dihydric phenol compound, wherein said dihydric phenol compound(s) are comprised of
(i) 2,2-bis(4-hydroxyphenyl) propane; and
(ii) bis-(4-hydroxyphenyl)terephthalamide in a range between about 1 weight percent and about 50 weight percent of the repeating units in the polycarbonate.
In this fifth aspect of the present invention, it is especially typical that the bis-(4-hydroxyphenyl)terephthalamide is utilized in an amount in a range between about 1 weight percent and about 20 weight percent, most preferably in a range between about 1 weight percent and about 15 weight percent of the repeating units in the polycarbonate. Alternatively, the meta isomer, i.e., bis-(3-hydroxyphenyl)terephthalamide can be utilized as a whole or partial replacement for the bis-(4-hydroxyphenyl)terephthalamide.
In each of these five aspects, the polycarbonate is typically comprised of BPA residues and residues of the comonomers as set forth herein. Accordingly, it is that Bisphenol A is utilized in an amount in a range between about 50 weight percent and about 99 weight percent of the repeating units in the polycarbonate.
Optionally, the polycarbonate may be further comprised of other dihydric phenol compound residues in an amount up to about 20 weight percent of the repeating units in the polycarbonate, thereby replacing the Bisphenol A, the comonomers, or combinations thereof, of the present invention in the total amount of dihydric phenol compounds utilized. Examples of such compounds include the following:
resorcinol
4-bromoresorcinol
hydroquinone
4,4xe2x80x2-dihydroxybiphenyl ether
4,4-thiodiphenol
1,6-dihydroxynaphthalene
2,6-dihydroxynaphthalene
bis(4-hydroxyphenyl)methane
bis(4-hydroxyphenyl)diphenylmethane
bis(4-hydroxyphenyl)-1-naphthylmethane
1,1-bis(4-hydroxyphenyl)ethane
1,1-bis(4-hydroxyphenyl)propane
1,2-bis(4-hydroxyphenyl)ethane
1,1-bis(4-hydroxyphenyl)-1-phenylethane
1,1-bis(3-methyl-4-hydroxyphenyl)-1-phenylethane
2-(4-hydroxyphenyl)-2-)3-hydroxypbenyl)propane
2,2-bis(4-hydroxyphenyl)butane
1,1-bis(4-hydroxyphenyl)isobutane
1,1-bis(4-hydroxyphenyl)decane
1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclobexane
1,1-bis(3,5-dibromo4-hydroxyphenyl)cyclohexane
1,1-bis(4-hydroxyphenyl)cyclohexane
1,1-bis(4-hydroxyphenyl)cyclododecane
1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclododecane
trans-2,3-bis(4-hydroxyphenyl)-2-butene
4,4-dihydroxy-3,3-dichlorodiphenyl ether
4,4-dihydroxy-2,5-dihydroxy diphenyl ether
2,2-bis(4-hydroxyphenyl)adamantine
xcex1, xcex1xe2x80x2-bis(4-hydroxyphenyl)toluene
bis(4-hydroxyphenyl)acetonitrile
2,2-bis(3-methyl-4-hydroxyphenyl)propane
2,2-bis(3-ethyl4-hydroxyphenyl)propane
2,2-bis(3-n-propyl4-hydroxyphenyl)propane
2,2-bis(3-isopropyl-4-hydroxyphenyl)propane
2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane
2,2-bis(3-t-butyl-4-hydroxyphenyl)propane
2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane
2,2-bis(3-aryl-4-hydroxyphenyl)propane
2,2-bis(3-methoxy-4-hydroxyphenyl)propane
2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane
2,2-bis(2,3,5,6-tetramethyl 4-hydroxyphenyl)propane
2,2-bis(3-5-dichloro-4-hydroxyphenyl)propane
2,2-bis(3 ,5-dibromo-4-hydroxyphenyl)propane
2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane
xcex1, xcex1-bis(4-hydroxyphenyl)toluene
xcex1, xcex1, xcex1xe2x80x2, xcex1xe2x80x2-Tetramethyl-xcex1, xcex1xe2x80x2-bis(4-hydroxyphenyl)-p-xylene
1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene
1,1-dibromo-2,2-bis(4-hydroxyphenyl)ethylene
1,1-dichloro-2,2-bis(5-phenoxy-4-hydroxyphenyl)ethylene
4,4xe2x80x2-di hydroxybenzophenone
3,3-bis(4-hydroxyphenyl)-2-butanone
1,6-bis(4-hydroxyphenyl)-1,6-hexanediol
ethylene glycol bis(4-hydroxyphenyl)ether
bis(4-hydroxyphenyl)ether
bis-(4-hydroxyphenyl)sulfide
bis(4-hydroxyphenyl)sulfoxide
bis(4-hydroxyphenyl)sulfone
bis(3,5-dimethyl-4-hydroxypbenyl)sulfone
9,9-bis(4-hydroxyphenyl)fluorene
2,7-dihydroxypyrene
6,6xe2x80x2-dihydroxy-3,3,3xe2x80x2,3xe2x80x2-tetramethylspiro(bis)indane(xe2x80x9cspirobiindane Bisphenolxe2x80x9d)
3,3-bis(4-hydroxyphenyl)phthalimide
2,6-dihydroxybenzene-p-dioxin
2,6-dihydroxythianthrene
2,7-dihydroxyphenoxathiin
2,7-dihydroxy-9,10-dimethylphenazine
3,6-dihydroxydibenzofuran
3,6-dihydroxydibenzothiophene
2,7-dihydroxycarbazole.
A further example of suitable dihydric phenols include those containing spirobiindane structural units such as those represented by the formula: 
wherein each R3 is independently selected from monovalent hydrocarbon radicals and halogen radicals; each R4, R5, R6, and R7 is independently C1-C6 alkyl; each R8 and R9 is independently H or C1-C6 alkyl; and each n is independently selected from positive integers having a value in a range between 0 and about 3, inclusive. The monovalent hydrocarbon radicals represented by R3 are preferably those containing in a range between about 1 carbon atom and about 12 carbon atoms, and include branched alkyl radicals and straight chain alkyl radicals. Some illustrative, non-limiting examples of these alkyl radicals include methyl, ethyl, propyl, isopropyl, butyl, tertiary-butyl, pentyl, neopentyl, and hexyl. Cycloalkyl radicals represented by R3 are preferably those containing in a range between about 3 ring carbon atoms and about 12 ring carbon atoms. Some illustrative non-limiting examples of these cycloalkyl radicals include cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, and cycloheptyl. Aryl radicals represented by R3 are preferably those containing in a range between about 6 ring carbon atoms and about 12 ring carbon atoms. Some illustrative non-limiting examples of these aryl radicals include phenyl, biphenyl, and napbthyl. Preferred aralkyl and alkaryl radicals represented by R3 are those containing in a range between about 7 carbon atoms and about 14 carbon atoms. These include, but are not limited to, benzyl, ethylphenyl, phenylbutyl, phenylpropyl, propylphenyl, and phenylethyl. The preferred halogen radicals represented by R 3are fluorine, chlorine and bromine.
In the dihydric phenols of the above formula, when more than one R3 substituent is present, they may be the same or different. The relative positions of the hydroxyl groups and R3 on the aromatic nuclear residues may be varied in the ortho or meta positions. The position of each hydroxy group is independently at any unsubstituted site on each of the aromatic rings.
The spirobiindane dihydric phenols of the above formula are compounds that are known in the art and are commercially available or may be readily prepared by known methods. Methods of preparation include those described in U.S. Pat. No. 4,701,566; and by R. F. Curtis and K. O. Lewis in Journal of the Chemical Society (England), 1962, p. 420; and by R. F. Curtis in Journal of the Chemical Society (England), 1962, p. 417. In one illustrative, non-limiting example, these spiro dihydric phenols may be conveniently prepared by (i) reacting two moles of a phenolic compound with one mole of a carbonyl-containing compound such as acetone, and (ii) thereafter co-reacting 3 moles of the product of (i) under acidic conditions to form the spiro dihydric phenol and 4 moles of a phenolic compound. The acids which may be utilized in (ii) can include acids as anhydrous methanesulfonic acid, anhydrous hydrochloric acid, and the like.
The most typical spiro dihydric phenol for forming polycarbonates is 6,6xe2x80x2-dihydroxy-3,3,3xe2x80x2,3xe2x80x2-tetramethyl-1,1xe2x80x2-spirobiindane (xe2x80x9cSBIxe2x80x9d), in which n in the above formula is 0 and the linkages with the rest of the polymer molecule are in a specific position on the aromatic rings.
The dihydric phenols (which are other than BPA and the comonomers in paragraph (ii) as set forth above) may be used alone or as mixtures of two or more dihydric phenols. Further illustrative examples of dihydric phenols include the dihydroxy-substituted aromatic hydrocarbons disclosed in U.S. Patent No. 4,217,438.
In addition, the present invention provides shaped, formed, or molded article comprising the polycarbonates of the first, second, third, fourth, and fifth aspects of the invention.
As noted above, the polycarbonates of the present invention may be prepared via the melt polymerization of dihydric phenol compounds and carbonic acid derivatives. In this regard, the carbonic acid derivatives will result in a repeat unit part structure which is merely a group of the formula 
Accordingly, the polycarbonates of the invention would possess structural units comprised of the following formulas: 
In the preparation of the polycarbonates of the present invention, especially typical diesters are the diesters of carbonic acid. As the diester of carbonic acid, various compounds may be used including, but not limited to, diaryl carbonate compounds, dialkyl carbonate compounds, and alkylaryl carbonate compounds. Typical diesters of carbonic acid include, but are not limited to, diphenyl carbonate; bis(4-t-butylphenyl)carbonate; bis(2,4-dichlorophenyl)carbonate; bis(2,4,6-trichlorophenyl)carbonate; bis(2-cyanophenyl)carbonate; bis(o-nitrophenyl)carbonate; ditolyl carbonate; m-cresol carbonate; dinaphthyl carbonate; bis(diphenyl)carbonate; diethylcarbonate; dimethyl carbonate; dibutyl carbonate; dicyclohexyl carbonate; and mixtures thereof. Of these, diphenyl carbonate is preferred. If two or more of these compounds are utilized, it is common that at least one is diphenyl carbonate.
Optionally, polyfunctional compounds may be utilized if the desired product is a branched polycarbonate. Such branched materials may be typical in certain applications, for example in films for packaging applications. Suitable polyfunctional compounds used in the polymerization of branched polycarbonate include, but are not limited to, 1,1,1-tris(4-hydroxyphenyl)ethane; 4-[4-[1,1-bis(4-hydroxyphenyl)-ethyl]-dimethylbenzyl]; trimellitic anhydride; trimellitic acid, or its acid chloride derivatives; trimethylolpropane; glycerol; and the like.
In the polycarbonates of the present invention, an end capping agent may optionally be used. Suitable end capping agents include monovalent aromatic hydroxy compounds, haloformate derivatives of monovalent aromatic hydroxy compounds, monovalent carboxylic acids, halide derivatives of monovalent carboxylic acids, and mixtures thereof.
Suitable end capping agents include, but are not limited to, phenol; p-tert-butylphenol; p-cumylphenol; p-cumylphenol carbonate; undecanoic acid; lauric acid; stearic acid; phenyl chloroformate; t-butyl phenyl chloroformate; p-cumyl chloroformate; chroman chloroformate; octyl phenyl; nonyl phenyl chloroformate; or a mixture thereof.
If present, the end capping agent is present in amounts in a range between about 0.01 moles and about 0.20 moles, typically in a range between about 0.02 moles and about 0.15 moles, even more typically in a range between about 0.02 and about 0.10 moles per 1 mole of the dihydric phenol.
In the practice of the present invention, a substantially equal molar mixture of the diester and the dihydric phenol compound is heated at atmospheric pressure in a substantially inert atmosphere at temperatures in a range between about 150xc2x0 C. and about 210xc2x0 C. Agitation of the mixture can be initiated as soon as the components start to melt. The system can be agitated slowly to promote better heat exchange. An effective amount of catalyst can be added at the outset of the reaction or after thermal equilibration, typically at the outset. An effective amount is in a range between about 1xc3x9710xe2x88x922 parts by weight and about 1xc3x9710xe2x88x926 parts by weight of the catalyst, per 100 parts by weight of the polycondensation mixture.
The resulting solution can be stirred until the catalyst has been dispersed and the reaction temperature of the mixture can be raised in a range between about 180xc2x0 C. and about 210xc2x0 C. while the pressure can be lowered to in a range between about 175 torr and about 250 torr. Distillation of aromatic hydroxy compound (i.e., the polycondensation by-product) can be effected and the pressure continuously reduced to further effect the separation of the aromatic hydroxy compound. The pressure of the reaction can be further reduced in a range between about 70 torr and about 130 torr while the temperature can be increased in a range between about 220xc2x0 C. and about 250xc2x0 C. The final stage of the reaction can be initiated by placing the condensation product under full vacuum at a pressure in a range between about 0.1 torr and about 5 torr and at a temperature in a range between about 270xc2x0 C. and about 350xc2x0 C. for in a range between about 0.5 hours and about 3 hours. Recovery of the final polycarbonate can be achieved after the theoretical amount of aromatic hydroxy compound has been collected.
The reaction conditions of the melt polymerization are not particularly limited and may be conducted in a wide range of operating conditions, hereinafter xe2x80x9cpolycarbonate melt polymerization conditionsxe2x80x9d. The reaction temperature is typically in a range between about 100xc2x0 C. and about 350xc2x0 C., more typically in a range between about 180xc2x0 C. and about 310xc2x0 C. The pressure may be at atmospheric, or at an added pressure in a range between atmospheric and about 15 torr in the initial stages of the reaction, and at a reduced pressure at later stages, for example in a range between about 0.2 torr and about 15 torr. The reaction time is generally in a range between about 0.1 hours and about 10 hours.
The melt polymerization may be accomplished in one or more stages. The catalysts of the present invention may be added in the same stage or different stages, if the melt polymerization is conducted in more than one stage.
In one embodiment of the present invention, the process is conducted as a two stage process. In the first stage of this embodiment, the catalyst, e.g., sodium hydroxide (NaOH), is introduced into the reaction system comprising the dihydric phenol compound and the diaryloxy compound. The first stage is conducted at a temperature of 270xc2x0 C. or lower, typically in a range between about 80xc2x0 C. and about 250xc2x0 C., more typically in a range between about 100xc2x0 C. and about 230xc2x0 C. The duration of the first stage is preferably in a range between 0 hours and about 5 hours, even more preferably in a range between 0 hours and about 3 hours at a pressure in a range between atmospheric pressure and about 100 torr, with a nitrogen atmosphere preferred.
In the second stage, the catalyst is introduced into the product from the first stage and further polycondensation is conducted. The catalyst may be added in its entire amount in the second stage, or it may be added in batches in the second and subsequent stages so that the total amount is within the aforementioned ranges.
It is typical in the second and subsequent stages of the polycondensation step for the reaction temperature to be raised while the reaction system is reduced in pressure compared to the first stage, thus bringing about a reaction between the dihydric phenol compound and the diaryloxy compound, and for the dihydric phenol and the diaryloxy compound finally to be subjected to a polycondensation reaction in a range between about 240xc2x0 C. and about 320xc2x0 C. under reduced pressure of 5 mm Hg or less, and typically 1 mm Hg or less.
If the melt polymerization is conducted in more than one stage, it is typical to add a base, such as tetramethylammonium hydroxide (TMAH) in an earlier stage than the catalyst of the present invention. In particular, it is typical to add the base to the reactor before the temperature reaches 220xc2x0 C., typically before it reaches 200xc2x0 C.
Additives may also be added to the polycarbonate product as long as they do not adversely affect the properties of the product. These additives include a wide range of substances that are conventionally added to the polycarbonates for a variety of purposes. Specific examples include heat stabilizers, epoxy compounds, ultraviolet absorbers, mold release agents, colorants, antistatic agents, slipping agents, anti-blocking agents, lubricants, antifogging agents, natural oils, synthetic oils, waxes, organic fillers, flame retardants, inorganic fillers and any other commonly known class of additives.
The reaction can be conducted as a batch, a semi-continuous, or a continuous process. Any desired apparatus can be used for the reaction. The material and the structure of the reactor used in the present invention is not particularly limited as long as the reactor has an ordinary capability of stirring. It is preferable that the reactor is capable of stirring in high viscosity conditions as the viscosity of the reaction system is increased in later stages of the reaction.
As noted above, certain comonomers of the invention impart improved hydrolytic stability to BPA-based polycarbonates. Thus, in a further aspect of the present invention, there is provided the use of the polycarbonates as set forth herein to produce shaped, formed or molded articles which are resistant to hydrolytic degradation. In a further embodiment of the present invention, there is provided the use of BUPT as a comonomer in BPA-based polycarbonates, as set forth herein, and the use of such polycarbonates as set forth herein to produce shaped, formed, or molded articles which are resistant to organic solvents.